The present invention concerns a room occupancy sensing apparatus. More particularly, but not exclusively, this invention concerns a building comprising a plurality of rooms and a room occupancy sensing apparatus, and a corresponding method for sensing room occupancy.
In various applications there is a desire to be able to detect which, if any, of a plurality of rooms are occupied. For example, such a function may be of particular use in quickly assessing which of many rooms in a building are occupied in the case of an emergency, such as a fire, or in detecting a burglar or other intruder or unauthorised person. Room occupancy sensing systems of the prior art are typically based on passive infrared sensors, which detect relatively large movements, and therefore occupancy, by means of monitoring a change in infra-red radiation from a moving heat source; however, such systems are not sufficiently sensitive for use in some applications: a relatively high background temperature in a room can adversely affect accuracy for example. For more sensitive applications, active sensor systems may be more appropriate. One such active sensor system uses radio frequency (RF) radiation and works by creating a field of radio wave radiation with one or more RF emitters and detecting changes in that field via one or more RF detectors. Such changes are caused by movement, which suggests occupancy in the associated room. The wavelength and power of such RF radiation can be chosen to suit the application, and can be chosen such that movement can be detected through walls in a building. The sensitivity and range of motion detection in such RF-based systems can be difficult to get right, however: increasing sensitivity can have the effect that motion in an adjacent room is detected through a wall, leading to false positive detections being made (e.g. suggesting incorrectly that there is motion within a room based on detecting motion in an adjacent room through a partition wall), whereas reducing sensitivity to the level where false positives are reduced to a reasonable level can risk rendering the motion detection system insufficiently sensitive to detect room occupancy reliably.
US2010/0053330 (Hellickson et al) describes a LADAR based security sensor system that operates by comparing a 3D LADAR image of a scene with a 3D template of the scene. When an intruder enters the scene the microprocessor detects a difference between the LADAR sensor output and the 3D template. Calibration of the system of US2010/0053330 is required, which accounts for the fixed objects within the scene, so as to create the pre-determined spatial reference template against which the spatial image information is compared. If any objects are moved (e.g., a chair when someone moves to a new location), the system needs to be recalibrated in order to avoid a false alarm. US2010/0053330 is a relatively complicated spatial imaging system for monitoring a single scene, for example a single room. Monitoring of multiple rooms would appear to require multiple systems. The methodology of US2010/0053330 relies on capturing a spatial image of a room, namely a 3-D image comprising multiple pixels. The system of US2010/0053330 relies on the detection of spatial information concerning the scene being monitored; this results in a system that would be relatively complicated and expensive for a room occupancy sensing system.
GB2128836 (Zellweger Uster AG) concerns monitoring discrete surfaces, particularly door or window openings of a building, against unauthorised intrusion. Directional radiation is emitted in pulses from a plurality of pulse transmitters, the transmitters being operated in a defined time sequence. Each transmitter emits several discrete beams at the same time in different directions, each beam travelling a different distance before being reflected by a surface and detected at a corresponding receiver. The transit times of the transmitted pulse for each of the beams from a single transmitter are representative of distance vectors. A change of any of the distance vectors is interpreted as an object penetrating into the space being monitored and interrupting the beam. In such a case, an alarm is triggered. The system of GB2128836 is able to determine the location of the object by means of ascertaining which distance vector has changed. Essentially, GB2128836 is performing a laser range-finding method with each beam emitted from each transmitter. The system relies on time-of-arrival information on a per beam basis. If it were the case that an object entered a room in a way that caused the times of arrival of two beams to switch (so that before the object enters the room, beam B1 has a time of arrival of T1 and beam B2 has a time of arrival of T2, whereas immediately after the object enters the room, beam B1 has a time of arrival of T2 and beam B2 has a time of arrival of T1) the apparatus would fail to detect the presence of the object. It therefore seems that the sensitivity of the method of GB2128836 could be improved. U.S. Pat. No. 4,319,332 also discloses a system similar to that of GB2128836.
GB2361058 (British Telecommunications plc) relates to an optical intruder detection system which utilises single-photon detection technology. Short multi-photon pulses of laser light are directed at a scattering target which scatters each pulse in all directions. The scattering target scatters photons throughout the room in all directions. Optical input ports are positioned in the room in various locations. Optical fibres of different lengths (introducing different respective optical delays) connect the input ports to a highly sensitive light detector in the form of a single-photon detector. In use, photons are reflected and received by respective input ports at different times (as a result of the optical delays introduced by the optical fibres) and then detected by the single-photon detector. In the steady state, a room in which there is no movement, will generate a photon-count rate at a certain level for each input port. A computer compares the measured count rates with predetermined upper and lower threshold values. When an intruder enters the room, and for example reduces the level of light reaching one or more of the input ports, the count rate will fall below the minimum expected threshold value. An intruder alarm is then triggered. The use of single-photon detection technology might at first be viewed as providing the system with excellent sensitivity; however, it is thought that the proposal's reliance on such detectors introduces several disadvantages. It would seem that the laser intensity would need to be finely adjusted so that each sensing node sends no more than a single photon to the detector at a time. This is because single photon detectors typically are unable to distinguish between a count event triggered by one photon and a count event triggered by many photons.
The prior art proposals known to the inventors tend to fall into one of two categories. There is either measurement and comparison of intensity/power (as in GB2361058 for example) and not range/time, or there is measurement and comparison of range/time (as in GB2128836 for example) and not intensity/power.
The present invention seeks to mitigate one or more of the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved room occupancy system, preferably one which provides improved sensitivity to small movements of, or caused by, an occupant in the room.